How to set up Postfix on ISPConfig?

Uhm I am running CentOS 5.2 to start with.
Anyway, I have also a e107 website up and running for 99 %....
The 1 % is like the problem; I can not get Postfix to run.
Can anyone give me a tutorial in how-to-set-up Postfix to send automails?
(Like the activationmail in e107 and other php mail() based e-mails...)
I'd like to know how it works...
(I am like 15 (16 at the 9th coming ) which means that I ain't that experienced regarding hosting...)

Uhm, I already have a CentOS 5.2 system running like you said before, also there is ISPConfig installed already.
Now:
1) The "vi" command doesn't work, how to fix that?
2) /etc/hosts does not exist - also a fix please.